Engine decompression device

ABSTRACT

A decompressing device for the firing chamber of an internal combustion engine during only low cranking speed, comprising a venting valve for the chamber, a housing therefor screwed to a port in the chamber, a valve element exposed to compressed gases in the chamber and forced temporarily thereby to a closed condition, and means for damping return opening action of the valve element whereby at and above a predetermined speed of the engine the valve element remains continuously closed.

I Unlted States Patent 1 1151 3,704,988 Steele Dec. 5, 1972 [541 ENGINEDECOMPRESSION DEVICE 3,335,711 8/1967 Roorda ..123/182 [72] Inventor:William Henry Steele, Milperra,

New south Australia Prlmary Exammer-Al Lawrence Smrth [73] AssigflfiyView Limited New South wales Attorney-Waters, Roditi, Schwartz & NissenAustraha 5 ABSTRACT [22] Filed: Sept 1970 A decompressing device for thefiring chamber of an [21] App[ 9,3 3 internal combustion engine duringonly low cranking speed, comprising a venting valve for the chamber, ahousing therefor screwed to a port in the chamber, a [if] (gill valveelement exposed to compressed gases in the Ed d [182 chamber'and forcedtemporarily thereby to a closed 8 0 u I I na e I u n v a l I e u e u sa: u u l I u u ac- [56] References Cited tion of the valve elementwhereby at and above a UNITED STATES PATENTS 854,035 5/1907l-lansen-Ellenhammer ..l23/l82 predetermined speed of the engine thevalve element remains continuously closed.

8 Claims, 5 Drawing Figures ENGINE DECOMPRESSION DEVICE This inventionrelates to decompression devices for the firing chambers of engines andparticularly those which restore compression within the engineautomatically.

There are two principal types of decompression devices presentlyavailable which function in this way. They either respond to the speedof the engine or to the count of engine revolutions. Decompressiondevices are invariably a venting valve and employ a mechanical interlockfor automatic closing to restore full compression conditions. Theseknown devices usually entail complex and/or delicate mechanisms eitherto count the engine strokes or to sense the engine speed. Furthermore,such valves frequently require to be manually set before starting of theengine is attempted. A further disadvantage of existing devices is thatthe transition between venting and closed conditions of the valve isabrupt.

It is the main object of this invention to provide a decompressiondevice for an engine which substantially avoids some or all of the abovedefects.

To this end the invention in its most general form is a device fordecompressing an internal combustion engine during cranking andautomatically progressively restoringcompression thereto as the runningspeed of the engine increases, said device comprising a housingmountable to a port in the engine compression chamber, venting means forthe housing for the escape of compressedgases in said chamber, a valveseat in the housing, and a valve element positioned and constructed soas to be forced to close upon the valve seat by the compressed gases in,and passing from, the chamber.

Preferred embodiments of the invention are illus trated in theaccompanying drawings in which:

FIG. 1 is a fragmentary side elevation of a typical engine cylindershown in half section and incorporating a first form of compressionrelease valve;

FIG. 2 is a similar view to FIG. 1 showing a second form of valveincorporating a dashpot, with the valve shown in its closed position;

FIG. 3 is a similar view of the embodiment of FIG. 2 showing the valvein an open position;

FIG. 4 is a similar view of an engine cylinder showing a third formcomprising a vacuum controlled valve in.

its closed position; and,

FIG. 5 is a similar view to FIG. 4 showing the same valve in an openposition.

A first preferred embodiment of the invention shown in FIG. 1 will nowbe described as applied to a two stroke engine 6, but it could also beadapted for four stroke engines. The decompression device 7 responds tothe velocity of gases forced through it during compression strokes ofthe engine 6 on which it is incorporated. The device is proportioned sothat certain minimum velocity of mixture passing through it is requiredto provide the pressure difference to raise it against its weight andthus close it. As described the device is assumed to be mountedsubstantially upright to utilize gravitational effect. Alternatively,the valve 8 of the device 7 may be closed against spring action.

To illustrate the principle behind the decompression device of thisinvention let it be assumed that the device consists of a tubular metalhousing 9 having a threaded reduced diameter portion 10 at one end topermit fixture of the device within a port 11 to the fir,- ing chamber12 of the engine 6, and a rod 12 extending axially through the housing9. A suitable form of vented bearing 13 is provided to support the rod12 for axial sliding movement. A valve seat 14 is formed in the threadedend 10 of the housing 9 and a valve head 15 is provided on that end ofthe rod 12 extending out of the housings threaded end 10. In the openposition of the valve 8, shown in FIG. 1, gases compressed within thefiring chamber are free to pass between the valve head 15 and its seat14, upwardly throughthe housing 9 and out of its vented upper end 16.Under such conditions full compression cannot occur within the chamberbut when th evalve head 15 is forced on to its seat 14 by the velocityof gases passing through thehousing 9 the firing chamber is no longervented to atmosphere and full compression therein can occur.

The velocity of the gases, composing the fuel mixture escaping throughthe valve 8, is at its greatest when the piston 17 is travelling at itshighest velocity during compression, i.e., when the piston 17 isslightly less than half-way through its stroke. When the piston 17, atthis point, is travelling at such a speed that the mixture velocitythrough the valve 8 is equal to or exceeds the minimum velocity requiredto close it, the valve 8 will close. It will remain closed until thepressure difference is reduced below the minimum required to hold thevalve 8 closed against its own weight. If the engine 6 did not fire onthis compression stroke, or on any subsequent stroke during the startingcycle, the valve 8 would re-open on the down stroke of the piston.

If, as is usual, the engine is being accelerated by the starting means,the piston 17 will betravelling faster, position for position, in eachsubsequent compression stroke in the starting cycle. This means that thevalve 8 will close earlier, resulting in greater compression in eachsubsequent compression stroke until the engine 6 starts or the startingcycle is completed.

During operation, i.e., running, of the engine 6 the conditions thatwill' cause the valve 8 to open may possibly occur when operating at lowspeed and low throttle opening. The-valve 8, under these conditions,will open on the down stroke of the piston 17 and allow airto be drawninto the cylinder. This will result in objectionable noise due to thepulsating flow and velocity of the induced air, and the possibility ofexplosions in the muffler due to the thinning out of the mixture.

However, it should be noted that this simple type of valve 8 may besatisfactory for an engine which is required to operate continuously athigh r.p.m. and/or which is always under sufficient load (i.e. does nothave to idle).

By increasing the back pressure in the muffler (not shown), or otherpart of the exhaust system,for the engine 6 during low speed or lowrunning, the valve 8 may be held closed due to the high cylinderpressure produced during the period that the exhaust port (not shown) ofthe engine 6 is open. This provision will entail that only duringcranking of the engine 6 will the valve 8 decompress the engine 5fiiring chamber.

The defects noted above can also be overcome by excluding air from beingsucked in through the hollow housing 9 on induction strokes of theengine, or at slow running speeds. By a second embodiment of theinvention this is achieved by arranging for the valve to remain closedthrough the initial portion of its downward travel and a damping deviceused to limit its movement within this closed portion of travel duringengine operating conditions. The use of an air dashpot 18 as shown inFIGS. 2 and 3, as the damping device is a very simple and mosteconomical solution. To provide for this the upper end of the rod 12A isprovided with a piston 19 fitted within a closed chamber 20 in the outerend of the housing 9A beyond venting slots 21 circumferentially providedin the wall of the housing 9A. The lower end 22 of the dashpot piston 19almost closes the vents 21 in its unoperated condition, as shown-in FIG.3. When operated, however, the piston 19 advances into the chamber 20 toforce the air therein back through the small clearance gap between thepiston 19 and the internal wall of the dashpot 18, so that return of thepiston is resisted by the resulting reduced pressure which would exist.For improved operation of the device it is .provided with anintermediate piston 23 operating within a reduced bore 24 of the housing9A beneath the venting means 21. Preferably, this piston 23 has atapered leading end 25 and in the closed condition of the valve 8A as inFIG. 2 it extends a short distance into the reduced bore 24. This willprovide for some degree of opening of the dashpot 18 before the openvalve 8A is connected to the venting means 21.

With the engine 6A not turning, the valve head A rests on a ledge 26 inthe engine head. As soon as the engine piston 17A begins to compress themixture in the cylinder, the valve head 15A rises so that mixture canescape past the underside of the dashpot piston 19. With increase ofvelocity of the escaping mixture, the valve head 15A rises until thepressure drops across the area of the intermediate 23, and the valvesection, to a minor extent, is such that the valve head 15Aprogressively closes under the influence of the compression in thecylinder.

With the engine running the dashpot 19 acts to ensure that the valve 8Aalthough it may be partly open is not vented. The intermediate piston 23has some clearance from its housing wall 27 but no appreciable amount ofair can be inducted into the chamber 24 until the piston 23 opens andthere is no accompanying objectionable noise.

A third form of the valve is shown in FIG. 4 and 5. In this form a valve88 is mounted in a housing 98 screwed into the engine cylinder 6B. Ahousing dish 28 is secured to the top of the housing 9B. Apertures 29for the admission of air are provided in the underside of the dish 28.An annular filter element 30 is secured within the dish 28 and airentering the apertures 29, passes through the filter 30 and into itshollow center 31. The air then passes down between the valve stem 12Band the housing 93 and into the engine cylinder 6B when the valve 88 isin its open position as shown in FIG. 5.

A flexible diaphragm 32 is stretched across the top of the dish 28 andclamped thereon by a domed cover 33. A flexible conduit 34 is secured toa spigot 35 mounted on top of the cover 33. The conduit 34 is alsoconnected to a tapping in the intake duct between the carburettorbutterfly and the inlet port (not shown) of the engine 6B.

When the engine 6B is stationary a spring 36, positioned between thecover 33 and diaphragm 32, forces the valve downwardly into contact witha step 26B in the compression chamber of the engine. As the engine iscranked air will pass in via the filter 30 and through the open valve 83as shown in FIG. 5. The movement of the engine piston (not shown) willlower the air pressure in the main intake ,(not shown) below atmosphereand this pressure drop will be conveyed to the space above the diaphragm32 and pressure below the diaphragm will force it up, against the actionof the spring 36, thus closing the valve 8B, and the engine 6B willproduce normal compression within the combustion chamber. With theengine running the reduced pressure in the intake du'ct will hold thevalve 88 closed as in FIG. 4.

It will be appreciated that the valve closing action of the diaphragm 32is initiated, in the case of a single cylinder engine, upon theinduction stroke of the engine piston which coincides with the openingof the valve 8B at low running speeds of the engine. Therefore, byappropriate design a good balance between both actions can be obtainedto ensure that even at a low running speed the engine is operating atmaximum efficiency.

The principal function of the valve holding devices of the invention isto ensure that the valve remains closed during running of the enginewhen on occasions the pressure in the firing chamber drops too lowduring the downstroke of the piston thus allowing atmospheric pressureon the valve from the outside to open the valve. These conditions occurtypically when the throttle in the carburetor has a low opening such asat idling or when it isclosed to slow the engine from'a high speed. Insuch cases the function of the diaphragm 32 is to use the low pressurein the inlet manifold to hold the valve 88 closed. However, the pressurein the inlet manifold is of a fluctuating nature, especially in engineswhich have few cylinders. In order to dampen these pulsations arestricting orifice 34A is inserted in the conduit 34 connecting thediaphragm 32 to the inlet manifold.

The low pressure on top of the diaphragm 32 causes atmospheric pressureon the other side to hold the valve 8B closed against the action of thelow pressure in the cylinder on the downstroke of the piston 17A.

The advantage of using a diaphragm for the function of holding the valveunder low pressure conditions in the cylinder is that such low pressureconditions typically occur at the same time as the lowest pressureconditions occur in the intake manifold, that is, under reduced throttleopenings with the engine running. It should be clear that thisexplanation of the diaphragm action applies to conditions obtaining withthe engine running, that is, after the engine has been started.

None of the valve holding devices of the invention are designed to haveany effective function during the starting of the engine. During thestarting of the engine each of the devices described is the same'inprinciple as the valve illustrated in FIG. 1. The only difference isthat in some cases a spring may be used instead of, or together with,relying upon the effects of gravity.

As an alternative to either of the above arrangements it may be possibleto provide one of the following:

1. A mechanical interlock (e.g. centrifugally operated) that will holdthe valve closed once the engine has started.

2. An electrical interlock that uses a solenoid, powered by an extracoil in the magneto, to hold the valve closed once a given rpm. isreached. The output from the coil in the magneto could either befiltered to give a substantially steady current or the impulses could bearranged to coincide with the instant the valve begins to drop.

From an understanding of the above description it will be seen that thedevice of the invention has the advantage that, due to the progressiveincrease in compression, the initial strokes are provided with less thanfull compression but still with sufficient to start the engine. Due tothe reduced compression less voltage is required to produce a spark atthe plug. As the magneto needs less speed to produce this reducedvoltage, the engine is thus able to start at a lower speed.

What I claim is:

1. A device for decompressing an internal combustion engine duringcranking and automatically progressively restoring compression theretoas the running speed of the engine increases, said device comprising ahousing mountable to a port in the engine compression chamber, ventingmeans for the housing for the escape of compressed gases in saidchamber, a valve seat in the housing, a valve element positioned andconstructed so as to be forced to close upon the valve seat by thecompressed gases in, and passing from, the chamber; a fluid chamber inthe housing, means for at least partly evacuating fluid from saidchamber; a displaceable member forming a wall of said chamber, and avalve stem interconnecting said displaceable member and said valveelement to hold said valve element closed when said fluid chamber is atleast partly evacuated.

2. A device according to claim 1, wherein said evacuating meanscomprises a fluid line for connecting the fluid chamber with the inletmanifold of the engine.

3. A device according to claim 2, wherein the displaceable member is adiaphragm.

4. A device according to claim 1, wherein the housing is tubular andthreaded at one end for screwing to said port, and the valve seat andthe valve element are located at the threaded end of the housing, andfurther comprising a dashpot located at the opposite end of the housingand containing said fluid chamber, said displaceable member being apiston for the dashpot, and said means for partly evacuating fluid fromthe dashpot chamber comprising clearance of the piston from the wall ofthe dashpot chamber.

5. A device according to claim 4, wherein an intermediate chamber isprovided in the tubular housing, an intermediate piston is provided onthe valve stem, and the venting means is located between the twochambers of the housing, said intermediate piston being so located onthe valve stem that it is accommodated in the intermediate chamber whenthe valve element is at least partly open.

6. A device for decompressing an internal combustion engine duringcranking and automatically progressively restoring compression theretoas the running speed of the engine increases, said device comprising atubular housing threaded at one end for screwing to a port in the enginecompression chamber, a valve seat located at the threaded end of thehousing, a valve element having a stem which passes axially throu h thehousing with said valve element protruding from he threaded end of thehousing so as to close upon the valve seat with the passage ofcompressed gases from the engine compression chamber into said housing,venting means in the housing for the escape of compressed gases therein,a fluid chamber at the other end of the housing, a diaphragm on an endof the valve stem and defining one wall of the fluid chamber, and afluid line having a restrictive orifice being connected to the fluidchamber and having means for connection to an inlet manifold of theinternal combustion engine, whereby reduced pressure in the intakemanifold serves to hold the valve element closed when the engine isrunning in excess of a predetermined speed.

7. A device according to claim 6, wherein the venting means is locatedbetween the diaphragm and the threaded end of the tubular housing, andcomprises an air filter. V

8. A device according to claim 6 including also a bias spring actingupon the valve stem to hold the valve element off the valve seat.

1. A device for decompressing an internal combustion engine duringcranking and automatically progressively restoring compression theretoas the running speed of the engine increases, said device comprising ahousing mountable to a port in the engine compression chamber, ventingmeans for the housing for the escape of compressed gases in saidchamber, a valve seat in the housing, a valve element positioned andconstructed so as to be forced to close upon the valve seat by thecompressed gases in, and passing from, the chamber; a fluid chamber inthe housing, means for at least partly evacuating fluid from saidchamber; a displaceable member forming a wall of said chamber, aNd avalve stem interconnecting said displaceable member and said valveelement to hold said valve element closed when said fluid chamber is atleast partly evacuated.
 2. A device according to claim 1, wherein saidevacuating means comprises a fluid line for connecting the fluid chamberwith the inlet manifold of the engine.
 3. A device according to claim 2,wherein the displaceable member is a diaphragm.
 4. A device according toclaim 1, wherein the housing is tubular and threaded at one end forscrewing to said port, and the valve seat and the valve element arelocated at the threaded end of the housing, and further comprising adashpot located at the opposite end of the housing and containing saidfluid chamber, said displaceable member being a piston for the dashpot,and said means for partly evacuating fluid from the dashpot chambercomprising clearance of the piston from the wall of the dashpot chamber.5. A device according to claim 4, wherein an intermediate chamber isprovided in the tubular housing, an intermediate piston is provided onthe valve stem, and the venting means is located between the twochambers of the housing, said intermediate piston being so located onthe valve stem that it is accommodated in the intermediate chamber whenthe valve element is at least partly open.
 6. A device for decompressingan internal combustion engine during cranking and automaticallyprogressively restoring compression thereto as the running speed of theengine increases, said device comprising a tubular housing threaded atone end for screwing to a port in the engine compression chamber, avalve seat located at the threaded end of the housing, a valve elementhaving a stem which passes axially through the housing with said valveelement protruding from the threaded end of the housing so as to closeupon the valve seat with the passage of compressed gases from the enginecompression chamber into said housing, venting means in the housing forthe escape of compressed gases therein, a fluid chamber at the other endof the housing, a diaphragm on an end of the valve stem and defining onewall of the fluid chamber, and a fluid line having a restrictive orificebeing connected to the fluid chamber and having means for connection toan inlet manifold of the internal combustion engine, whereby reducedpressure in the intake manifold serves to hold the valve element closedwhen the engine is running in excess of a predetermined speed.
 7. Adevice according to claim 6, wherein the venting means is locatedbetween the diaphragm and the threaded end of the tubular housing, andcomprises an air filter.
 8. A device according to claim 6 including alsoa bias spring acting upon the valve stem to hold the valve element offthe valve seat.